(643f) Impact of Carbon Number of Carboxylic Acid on the Polarity of Hydrophobic Deep Eutectic Solvent

Solvatochromic dyes offer a powerful look into the molecular forces that exist in solutions. Zwitterionic dyes are particularly useful for the investigation of hydrophobic deep eutectic solvents (HDES), which interact via a hydrogen bond. This bond results in a solution with a melting point significantly lower than that of either hydrogen bond acceptor (typically a quaternary ammonium salt) or donator. The hydrogen bond donor, which is usually a carboxylic acid for hydrophobic deep eutectic solvents, is extremely influential on this melting point, with octanoic acid based HDES being liquid at room temperature and dodecanoic acid HDES being a solid until 35-45 °C. By taking advantage of this phenomena, the hydrogen bond acceptor can be changed to impact physical properties like Henry’s law constants without dramatically changing polarity or melting point of the solvent. COSMOTherm, a density functional theory based molecular modeling software, is used to explore the impact of carboxylic acid length on the sensitivity of HDES systems to change in N-quaternary ammonium bromide salt characteristics. These results are verified using solvatochromic dyes 4-nitroaniline and 4,4 N-diethyl 4-nitroaniline.